Often used to describe a situation or set of circumstances that are so unlikely as to never be thought of. WATFO's are often used to set up situations in movies that would otherwise never happen. In this context is can be used to mean 'contrived'.

...so I get hit by a second car a block later. I mean, I've never been hit and twice in 2 blocks? WATFO?

We'll use a WATFO to send the main character to Japan. Something like, he has the leave the US after getting arrested for street racing and his dad is over there in the Navy. (As used in from Fast and the Furious 3: Tokyo Drift)